DNP for polarizing liquid 3 He DNP for polarizing liquid 3 He Hideaki Uematsu Department of Physics Yamagata University

Member(2006) T.Shishido, T.Iwata, S.Kato, T.Michigami, S.Ohizumi, Y.Tajima, A.Tanaka, K.Toyama, H.Uematsu, and H.Y.Yoshida Department of Physics, Yamagata University, Yamagata N.Kuriyama Department of Material and Biological Chemistry, Yamagata University, Yamagata

Background of the study Polarized 3 He targets have been used in various scattering experiments Polarized 3 He targets have been used in various scattering experiments > In 3 He only neutron is polarized > In 3 He only neutron is polarized > A good target for the study of neutron characteristics > A good target for the study of neutron characteristics > Studied only in gas targets > Studied only in gas targets Advantages of polarizing liquid 3 He Advantages of polarizing liquid 3 He >Density ⇒ := 1 : 662 >Density ⇒ gas:liquid= 1 : 662 >Its fluidity may allow to make a polarized target with circulating polarized liquid 3 He >Its fluidity may allow to make a polarized target with circulating polarized liquid 3 He >Could be applied in many other fields >Could be applied in many other fields (e.g. medical use, material science, etc.) (e.g. medical use, material science, etc.)

How to obtain polarized liquid 3 He 1. From polarized solid 3 He >Polarized liquid is obtained by quickly melting polarized solid >Polarized liquid is obtained by quickly melting polarized solid >55% polarization obtained in solid at 6.6T, 6mK, and 30bar, G.Bonfait et al. Phys.Rev.Lett. 53(1984)1092 >55% polarization obtained in solid at 6.6T, 6mK, and 30bar, G.Bonfait et al. Phys.Rev.Lett. 53(1984)1092 → required special equipments to make 3 He solid → required special equipments to make 3 He solid 2. Dynamic Nuclear Polarization (DNP) > spin-spin coupling between electron and nucleus > spin-spin coupling between electron and nucleus >Transferring polarization of electrons to neighboring nuclei >Transferring polarization of electrons to neighboring nuclei >Both positive and negative polarization available >Both positive and negative polarization available

US group applied DNP for polarizing liquid 3 He powdered sucrose charcoal powdered sucrose charcoal Polarization process: Polarization process: electron → 1 H → 3 He of TE signal amplitude 1.18 times of TE signal amplitude (T= 1.8 K, B= 182 G) Relaxation time Relaxation time T 1 = 1.02sec L.W.Engel et al. L.W.Engel et al. Phys. Rev. B 33, 2035 (1986) DNP Polarization transfer H↑H↑ e charcoal Liq. 3 He RF

fluorocarbon beads containing electronic paramagnetic centers fluorocarbon beads containing electronic paramagnetic centers Polarization process: Polarization process: electron → 19 F → 3 He a. Positive: of TE signal at a. Positive: twice of TE signal at T= 250 mK, B= 300 G b. Negative: not mentioned A.Schuhl et al. A.Schuhl et al. Phys. Rev. Lett. 54,1952 (1985) French group applied DNP for polarizing liquid 3 He DNP 3 He 19 F H TE 3 He Polarization transfer F↑F↑ e fluorocarbon Liq. 3 He RF

Our New DNP method for polarizing liquid 3 He Direct coupling between electron and 3 He Direct coupling between electron and 3 He Using unpaired electrons in free radical Using unpaired electrons in free radical Embedding free radicals into porous material Embedding free radicals into porous material Filling the porous material with liquid 3 He Filling the porous material with liquid 3 He Microwave irradiation Microwave irradiation  Free radical →  Free radical → TEMPO  Porous material →  Porous material → Zeolite

Zeolite and TEMPO NaY type zeolite (n=51) NaY type zeolite (n=51) Super Cage Max dia.: 13Å Window dia.: 7.4Å 4.7x10 19 super cages/g A super cage can store 80 3 He atoms TEMPO (2,2,6,6-tetramenthyl- piperidinyl-1-oxyle) TEMPO (2,2,6,6-tetramenthyl- piperidinyl-1-oxyle) Melting point: 36 º C Boiling point: 67 º C Molecule size: ~7Å sodalite cage double T6-ring Zeolite(Na n Al n Si (192-n) O 384 ·240H 2 O (n=48~76 ) HH CH 3 H3CH3C H3CH3C H H H H N O TEMPO 7Å7Å 7.4Å ESR signal of TEMPO in zeolite super cage

Embedding TEMPO to Zeolite Preparation : Desiccate zeolite at 500 ºC for 8 hours Preparation : Desiccate zeolite at 500 ºC for 8 hours 1. Dissolve TEMPO in n- pentane 2. Add zeolite powder to n- pentane solution 3. Stir n-pentane solution for 8 hours in a sealed vessel 4. Evaporate n-pentane in a vacuum container 500 ºC Zeolite

Embedding TEMPO to Zeolite TEMPO n-pentane Preparation : Desiccate zeolite at 500 ºC for 8 hours Preparation : Desiccate zeolite at 500 ºC for 8 hours 1. Dissolve TEMPO in n- pentane 2. Add zeolite powder to n- pentane solution 3. Stir n-pentane solution for 8 hours in a sealed vessel 4. Evaporate n-pentane in a vacuum container zeolite

Embedding TEMPO to Zeolite Preparation : Desiccate zeolite at 500 ºC for 8 hours Preparation : Desiccate zeolite at 500 ºC for 8 hours 1. Dissolve TEMPO in n- pentane 2. Add zeolite powder to n- pentane solution 3. Stir n-pentane solution for 8 hours in a sealed vessel 4. Evaporate n-pentane in a vacuum container

Embedding TEMPO to Zeolite Preparation : Desiccate zeolite at 500 ºC for 8 hours Preparation : Desiccate zeolite at 500 ºC for 8 hours 1. Dissolve TEMPO in n- pentane 2. Add zeolite powder to n- pentane solution 3. Stir n-pentane solution for 8 hours in a sealed vessel 4. Evaporate n-pentane in a vacuum container pump

Experimental setup  Experimental cell made of a PET tube and a VCR gas connector  Volume : 2.5cc (L=35mm, φ=9mm)  Experimental cell filled with zeolite tightly and quickly Experimental cell experimental chamber

Thermal equilibrium signal of 3 He T= 1.42 K, B ≒ 2.5 T 1.3×10 19 electron spins/cc T= 1.47 K, B ≒ 2.5 T Low spin density (with zeolite) 0.45×10 19 electron spins/cc T= 1.54 K, B ≒ 2.5 T High spin density (with zeolite)Bulk 3 He (without zeolite) Symmetric signal when 3 He in zeolite Symmetric signal when 3 He in zeolite Narrower width for low spin density Narrower width for low spin density Bulk 3 He signal shows asymmetric shape Bulk 3 He signal shows asymmetric shape

TE signals fitted with Lorentzian T= 1.42 K,B ≒ 2.5 T 1.3×10 19 spins/cc T= 1.47 K, B ≒ 2.5 T 0.45×10 19 spins/cc T= 1.54 K, B ≒ 2.5 T Extent: 44.4 ppm Bulk 3He(without zeolite) Center frequency of 3 He: Center frequency of 3 He: f c = 81.09MHz (at 2.5T) Extent: 202 ppm High spin density (with zeolite)Low spin density (with zeolite) FWHM ※ Extent=FWHM/f c

Relaxation time of liquid 3 He Fitting function S: area of the NMR signal Time development of NMR signal of liquid 3 He inside zeolite, spin density: T= 1.44 K, B= 2.5 T, spin density: 1.3×10 19 spin/cc Relaxation time: Relaxation time: T 1 = 330 sec. 3 He in zeolite with TEMPO

Positive enhancement by DNP TE signal T= 1.48 K, B ≒ 2.5 T max polarized signal B ≒ 2.5 T observed positive enhancement observed positive enhancement S/S TE = 2.34 spin density= (low concentration) spin density= 0.45×10 19 (low concentration)

Negative enhancement by DNP TE signal T= 1.53 K, B ≒ 2.5 T max polarized signal B ≒ 2.5 T observed negative enhancement S/S TE =-1.59 spin density= spin density= 0.45× polarized TE

Microwave frequency dependence fc: ESR center frequency of TEMPO(=70.22GHz) of TEMPO(=70.22GHz) spin density: spin density: 1.3×10 19, B ≒ 2.5T Frequency difference(250MHz) between max enhancement points is smaller than that expected from the calculated ESR line width( 340 MHz ※ ) ※ S.T.Gortez, et al. Nucl. Instrum. and Meth A526, 43 (2004) 250MHz 340MHz

Summary We observed the thermal equilibrium signals of liquid 3 He in zeolite. We observed the thermal equilibrium signals of liquid 3 He in zeolite. A narrow signal was observed with low electron spin density. A narrow signal was observed with low electron spin density. We measured relaxation time of 3 He in zeolite (a few minutes at 2.5T) We measured relaxation time of 3 He in zeolite (a few minutes at 2.5T) We obtained polarization enhancements for liquid 3 He in zeolite by DNP. We obtained polarization enhancements for liquid 3 He in zeolite by DNP.  The enhancements were larger than ever before (obtained by DNP).  They may be improved by tuning the conditions.

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Zeolite and its character Mineral which has a micro-porous structure, high hydrophobicity, thermostability and mostly used as a catalyst, ion exchanger, absorber Mineral which has a micro-porous structure, high hydrophobicity, thermostability and mostly used as a catalyst, ion exchanger, absorber (Na n Al n Si (192-n) O 384 ·240H 2 O (n=48~76 ) (Na n Al n Si (192-n) O 384 ·240H 2 O (n=48~76 ) Used (HSZ-300serise)TOSOH corporation Used (HSZ-300serise)TOSOH corporation Cation type: Na Cation type: Na SiO 2 /Al 2 O 3 (mol/mol): 5.5 SiO 2 /Al 2 O 3 (mol/mol): 5.5 Na2O(wt%): 12.5 Na2O(wt%): 12.5 U.C.C. by ASTM :24.63 U.C.C. by ASTM :24.63 NH3-TPD(mmol/g): - NH3-TPD(mmol/g): - Surface Area(BET, m2/g): 700 Surface Area(BET, m2/g): 700 Crystal Size(μm): 0.3 Crystal Size(μm): 0.3 Mean Particle Size(μm): 6 Mean Particle Size(μm): 6

Zeolite’s atom atomspin Magnetic moment Abundance(%) 16 O O 5/ O Na 3/ Al 5/ Si Si 1/ Si

Decrease of TEMPO in Zeolite Spin density :7.5×10 18 spin/cc Room temperature

n-pentane C 5 H 12 C 5 H 12 melting point: -131ºC melting point: -131ºC boiling point: 36.07ºC boiling point: 36.07ºC →0.13% Density of liquid 3 He in 1g zeolite in 1g zeolite23.1mg